The present invention, in some embodiments thereof, relates to apparatus and a method for data transmission over power lines and, more particularly, but not exclusively, to such data transmission wherein the power lines are multi-phase.
The history of communication over power lines begins with narrowband power line communications and this appeared soon after the beginning of wide-spread electrical power supply. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines in the frequency range 15 to 500 kHz for telemetry purposes, and this continues to the present time.
In the 1930s, ripple carrier signaling was introduced on the medium (10-20 kV) and low voltage (240/415V) distribution systems. For many years the search has been going on for a cost effective bi-directional technology suitable for applications such as remote meter reading. For example, the Tokyo Electric Power Co was running experiments in the 1970's which reported successful bi-directional operation with several hundred units. Since the mid-eighties there has been a surge of interest in using the potential of digital communications techniques and digital signal processing.
Broadband over power lines (BPL), also known as power-line Internet or Powerband, is the use of power line communication technology to carry radio signals for communication purposes, and in particular, to provide broadband Internet access through ordinary power lines. An aim of BPL is that a computer, or any other communication device, would need only to plug a BPL modem into any outlet in an equipped building to have high-speed Internet access.
BPL has an advantage in that the extensive infrastructure already available would appear to allow people in remote locations to have access to data networks, such as the Internet, with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up to such a network.
Modern BPL systems typically use OFDM modulation which is effective in the high noise environment of the power line and also allows the mitigation of interference with radio services by removing specific frequencies used. The present teachings are however general to any kind of modulation found to be suitable.
The electrical distribution system is multi-phase. In some countries it is usual for a single domestic premises to receive just a single phase, and in other countries it is usual for them to receive two or three phases. Even in cases where the premises receive three phases, most power outlets carry only a single phase plus the neutral line. Typically the premises would be wired so that different areas thereof receive different phases. Any given computer or electric device in such a premise would therefore be connected to one of the three phases, and the signal for that device would be sent through that phase. This raises the problem that, for example, a computer located in a particular part of a building where it is connected to a given phase, could not be moved to another part of the building unless the phase used in that part of the building is also identified and configured for communication.